DESCRIPTION: Previous experiments supported by this research grant have demonstrated that 2-chlorodeoxyadenosine (CdA) shortens the survival of normal and malignant lymphocytes in Go/G1 phase. Consequently, CdA is an effective agent for the treatment of both lymphoproliferative and autoimmune diseases. The sphingomyelin metabolite ceramide has been proposed to be a common cytoplasmic mediator of cell injury. Therefore, the principal investigator and his colleagues synthesized potential low molecular weight antagonists of ceramide, and found that these compounds did increase the resistance of quiescent lymphocytes to CdA. Hence, the ceramide antagonists also prolonged normal lymphocyte survival, protected lymphocytes from ultraviolet radiation-induced apoptosis, and sensitized fibroblasts, glial and endothelial cells to growth and survival factors. Structure-activities showed that the active compounds specifically antagonized ceramide activation of purified protein phosphatase 2A (PP2A), without affecting basal enzyme activity. Based upon these observations, this renewal grant application proposes: (1) to determine more precisely the structural basis for antagonism of ceramide activated PP2A, (2) to delineate the role of ceramide metabolism in the toxicity of CdA, and related nucleoside antimetabolites to normal and malignant lymphocytes, (3) to use the antagonists to pinpoint the protein targets of ceramide-activated PP2A in growth arrested or dying cells, (4) to pursue the development of low molecular weight agonists of PP2A, and (5) to study how the ceramide antagonists and agonists regulate the survival of normal and malignant lymphocytes in vivo. The long-term goals of these studies are to understand the metabolic regulation of senescence and apoptosis in lymphocytes, and to devise new agents for the treatment of lymphoproliferative and immunodeficiency diseases.